This invention relates to primary-aliphatic (alkyl, cycloalkyl and aralkyl) azoalkanes containing one .alpha.-hydroxy substituent per azo group which are more thermally stable than corresponding tertiary azo compounds such as those disclosed in our Canadian Pat. No. 924,299 and therefore operate as vinyl polymerization initiators or curing agents for resins at higher temperatures. The new compounds hereof are also useful for preparing cellular structures from a variety of polymers as is more fully described in MacLeay et al. U.S. Application Ser. No. 453,446, now abandoned filed concurrently herewith.
So far as is known, none of the compounds hereof have been disclosed heretofore. Symmetrical .alpha.,.alpha.'-dihydroxyazoalkanes have been reported to form but are very unstable and essentially unisolatable [E. Schmitz, R. Ohme and E. Schramm, Ann. 702, 131 (1967)]. Consequently, they were not reported to be of any special value except as generators of diimide. Freeman and Rathjen, [J. Org. Chem. 37, 1686(1972)] reported the synthesis of 3-hydroxy-1-pyrazolines, cyclic examples of .alpha.-azocarbinols, by hydrolysis or hydrogenolysis of 3-acetoxy-1-pyrazolines. These carbinols are reported to undergo both acid and base-catalyzed ring opening to give ketones; no utility is reported for them.
T-Butyl-.alpha.-hydroxyalkyldiazenes have been prepared from t-butyldiazenes and aldehydes [S. Hunig and G. Buttner, Agnew. Chemie. Int. Ed. 8, 451(1969)], and from alkoxydiazenium salts and hydroxide ion [S. Hunig and G. Buttner, Chem. Ber. 104, 1088(1971)]. In the latter article Hunig and Buttner also prepared the following primary alkyl-.alpha.-hydroxyalkyldiazenes: 1-neopentylazo-1-hydroxymethane, 1-ethylazo-1-hydroxyethane, 1-methyl-azo-1-hydroxymethane, 1-ethylazo-1-hydroxymethane, and 1-methylazo-1-hydroxy-2,2-dimethylpropane. These prior art compounds do not foam the polyester resins nearly as efficiently as the hydroxy-azos hereof wherein the carbon attached to both the azo group and hydroxyl group is tertiary. In fact, as is developed more particularly herein, the azo compounds of this invention functioned effectively to foam polyesters where these prior art compounds failed entirely.
t-Alkyl-.alpha.-hydroxyazoalkanes [MacLeay et al. U.S. Application Ser. No. 149,041, filed June 1971], now abandoned and sec-alkyl-.alpha.-hydroxyazoalkanes [MacLeay et al. U.S. Application Ser. No. 453,447 filed concurrently herewith -- ] are known. Their use in foaming resins is disclosed and claimed in MacLeay et al. U.S. Application Ser. No. 453,466. The primary-aliphatic-.alpha.-hydroxyazoalkanes hereof are very similar to the t-alkyl and sec-alkyl-.alpha.-hydroxyazoalkanes in their chemical properties except that the substitution of a primary-alkyl group for a t-alkyl or sec-alkyl group increases the thermal stability of the azo compound. In fact, the t-alkyl-.alpha.-hydroxyazoalkanes must be refrigerated to below 0.degree. C. in order to maintain assay.
It is unobvious to prepare the novel I compounds based on the Prior Art. The methods used to prepare the known t-butyl-.alpha.-hydroxyalkyldiazenes do not apply. They were prepared from t-butyldiazenes and aldehydes [S. Hunig and G. Buttner, Agnew. Chemie Int. Ed. 8, 451(1969)] and from alkoxydiazenium salts and hydroxide ion [S. Hunig and G. Buttner, Chem. Ber. 104, 1088(1971)]. The alkoxydiazenium salts are derived from aldehydes.
In the latter article Hunig and Buttner also prepared some primary alkyl-.alpha.-hydroxyalkyldiazenes but again these compounds were derived from aldehydes. They did not and could not prepare alkyl-.alpha.-hydroxyldiazenes of this invention using the reactions they employed. Since Hunig et al. did not describe any use for their compounds, it was not obvious that the compounds of this invention would foam resins. In addition from the prior art there was no indication that the compound of this invention (derived from ketones) would be more efficient foaming agents than the .alpha.-hydroxyalkyldiazenes (derived from aldehydes) of the prior art.
MacLeay et al. U.S. application Ser. No. 149,041, supra, describes the synthesis of 2-t-butylazo-2-hydroxy-4-methylpentane by reacting 2-t-butylazo-2-chloro-4-methylpentane with sodium hydroxide. An attempt made to prepare the primary-alkyl-.alpha.-hydroxyazoalkanes by this method was unsuccessful in that the appropriate intermediate primary-alkyl-.alpha.-chloroazoalkanes could not be prepared by the method. Therefore a new method had to be devised. After intense investigation the reduction method described herein (and more particularly disclosed and claimed in MacLeay U.S. Application Ser. No. 453,451 now abandoned filed concurrently herewith, the contents of which are incorporated herein by reference) was developed.
The reduction of azohydroperoxides, where the azo and hydroperoxide groups are linked to the same carbon, was novel. It was found that the reduction had to be carried out on the basic side to prevent the acid decomposition of the azohydroperoxide.